A conventional inkjet printer prints images by ejecting ink droplets onto a recording medium being conveyed in a prescribed direction. The conventional printer is equipped with a line-type inkjet head having a plurality of nozzles aligned in a width direction of the recording medium.
More specifically, the inkjet head has a plurality of head units (head modules) arranged in two rows that extend in the width direction of the recording medium (direction of alignment). The positions of the head units in the two unit rows are shifted from each other in the direction of alignment. Further, the layout range of nozzles in a head unit belonging to one unit row partially overlaps the layout range of nozzles in a head unit belonging to the other unit row in the conveying direction of the recording medium. Note that the head units constituting a single unit row are arranged at equal intervals in the alignment direction. Thus, any two head units of different unit rows that overlap in the conveying direction have the same amount of overlap regardless of the positions of the head units in the alignment direction.
Each head unit has a plurality of channel modules in which are formed nozzles and pressure chambers, and a plurality of actuator modules having piezoelectric elements corresponding to the pressure chambers in the channel modules. Each piezoelectric element in the actuator module has a piezoelectric layer, and two types of electrodes disposed one on either side of the piezoelectric layer. The piezoelectric element utilizes deformation generated in the piezoelectric layer (piezoelectric strain) when a prescribed drive voltage is applied across the two types of electrodes to generate a pressure wave in the corresponding pressure chamber of the channel module in order to eject ink from the corresponding nozzle.
The following method of assembling an inkjet head has also been employed in order to suppress variations in ink temperature among inkjet heads. First, the capacitance of each actuator module is measured, and the modules are ranked based on the magnitude of their capacitance. When assembling the inkjet heads, the modules are arranged according to their assigned ranks. Specifically, modules having a high capacitance generate a greater amount of heat than modules with low capacitance. Therefore, modules having high capacitance are arranged at end positions that are more easily cooled, while modules having low capacitance are arranged at center positions less conducive to cooling.